/Engine/Source/Runtime/GeometryCore/Public/DynamicMesh/DynamicMesh3.h
Remove a triangle from the mesh. Also removes any unreferenced edges after tri is removed. If bRemoveIsolatedVertices is true, then if you remove all tris from a vert, that vert is also removed. If bPreserveManifold, we check that you will not create a bow tie vertex (and return false). If this check is not done, you have to make sure you don't create a bow tie, because other code assumes we don't have bow ties, and will not handle it properly
[EMeshResult](API\Runtime\GeometryCore\UE__Geometry__EMeshResult) RemoveTriangle ( int TriangleID, bool bRemoveIsolatedVertices, bool bPreserveManifold )